The present technology relates to a communication device and a communication system that perform data communication by using a human body as a medium. Especially, the present technology relates to a communication device and a communication system that perform human body communication of an electric field communication system by mainly using a human body's property as a dielectric.
Two or more information devices can communicate with each other through various media such as a wire and a radio. A human body communication technology in which a human body is incorporated in a transmission channel has recently begun to attract lots of attention. Human body communication does not use a communication cable so as to be conveniently used in music data transmission between a portable music reproduction device and a head phone, for example. Further, in the human body communication, a communication signal passes through a body of a user and therefore information is hardly leaked. Accordingly, the human body communication can be used in secret communication such as personal authentication and account settlement, as well.
A human body has a property as a conductor and a property as a dielectric. A human body communication system using the property as a conductor is called a current type human body communication system. In the current type human body communication system, a transmission/reception electrode has to constantly contact with a human body, so that a user feels strangeness or discomfort. Thus, there is a problem in usability. Further, a human body communication system using the human body's property as a dielectric is called an electric field human body communication system. In this case, between transmission/reception electrodes which are disposed to interpose a human body therebetween, one of a radiation electric field which transmits in space, a dielectric electromagnetic field, and a quasi-electrostatic field which uses electrification of a human body (not propagation) is formed and a signal can be transmitted based on potential difference which acts in such field.
A human body communication system is commonly composed of a human body side communication device which is attached in a manner to contact with a human body skin and an apparatus side communication device which is installed near the human body. The human body side communication device is a portable terminal such as a cellular phone and a personal digital assistant (PDA) and an electrode of the portable terminal contacts with a human body skin in a state that a user carries the portable terminal. When a predetermined part such as a fingertip of a user touches an electrode of the apparatus side communication device, data is transmitted.
For example, Japanese Unexamined Patent Application Publication No. 2006-318067 and Japanese Unexamined Patent Application Publication No. 2009-245402 propose an apparatus side communication device used in human body communication. In the apparatus side communication device, a touch panel is provided, and a transparent electrode is superposed on a data display unit of the touch panel or a low-resistive peripheral electrode is closely disposed in a manner to surround a periphery of a surface which a fingertip touches. The apparatus side communication device performs the human body communication by using an input operation which is performed by a user with respect to the touch panel with his/her fingertip. According to a human body communication system using such apparatus side communication device of the touch panel type, human body communication is performed while a user performs a touch panel operation with his/her fingertip in a manner to follow an indication of a display. Thus, data can be efficiently processed.
However, the human body communication is easily affected by a ground and therefore communication is unstable disadvantageously. Further, an electrode superposed on a touch panel is easily affected by surrounding metal or noise. Therefore, it is concerned that data communication becomes unstable due to the size of a touch panel depending on the installation site of an apparatus side communication device.
In an application example such as user authentication, a size of communication data is small and processing is completed in a short amount of time, so that communication stability is not such a big matter. On the other hand, in an application example in which large-volume data such as music data and moving image data is transmitted in a certain period of time, communication stability is an important matter.